I also had the bright idea to try this on library computers and email kiosks around campus used by thousands of students. Rather than booting into Ophcrack I'd just log in with the admin account and run pwdump from a USB stick to collect password hashes. I figured out how to enumerate Windows machines over the network using NetBIOS and ran the pwdump utility remotely using psexec, so that I could hit every computer in the library at once, or every computer in a computer lab, etc.
I ended up cracking credentials for most students and faculty on the entire campus. I was really young at the time and thought this was some real cool James Bond shit. I never once used it for evil: never read anyone's email, never viewed anyone's private files, never poked around the academic file shares for test solutions, never tried to steal credit card numbers or social security numbers from the finance office's file share. It was purely a hack for the thrill of breaking down barriers and outsmarting the security. But MONTHS later after I had long since grown tired of tinkering with this stuff, a couple of uniformed police officers pulled me out of Calculus class and took me downtown. They tossed my dorm room and confiscated my computer and my phone and every piece of digital storage I owned. The school threw the book at me, I guess because they were so embarrassed by their incompetence on display from being beaten by a 16 year old.
(Posting on my alt account for obvious reasons.)